I'm working on an art installation that has a lot of 12V LED lights triggered by PIR motion sensors. The current motion sensors we have work but not that well because it switches on for a set duration of 7 seconds and there is no way to adjust that. It also lacks a few functions that we'd like to have, such as a sensitivity adjustment for the PIR motion detector. I think this diagram explains best what I'd like to accomplish:

A Google search tells me this product best replicates the functions that I'd like:http://www.uk-automation.co.uk/products/Motion-Sensor-PIR-Light-Switch-(180-Deg.).html
However, I'd like the ability to slowly ramp up the voltage to the LED lights when the switch goes on and have it fade when the switch goes to the off position. The ability to adjust how fast it ramps up and down is important too. I should be able to adjust everything without the use of a computer, so something like turning a physical knob or pressing buttons to change settings would be great. It also needs to work in bright lights. The PIR switch I have currently works only in dim lights so when it switches the lights on, it goes on an infinite loop and won't turn off.

Finally, the device needs to be robust and reliable. I don't want to have to change batteries or for it to lose its programming at any point.

I was wondering if anyone here can give me some advice on the best way to put something like this together or if they would be willing to construct this for a flat fee. Thanks so much for any helpful advice.